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Die Casting of Zinc Alloy Purification Treatment

  • Refining and purification are important steps in the production of pure and high-quality zinc alloy die casting parts. Static clarification, chloride treatment, inert gas blowing, and filtration are all methods of purifying zinc alloy. In this article, we will discuss some of the most common purification treatment methods for zinc alloy die casting.

    Purification Treatment for Zinc Alloy Die Casting 

    1. Chloride treatment
    One of the most widely used methods is chloride treatment. After the alloy has been melted, add 0.1% – 0.2% chlorination or 3% – 4% hexachloroethane to the bell jar and stir slowly.

    2. Metal liquid through a fine ceramic filter
    A better purification effect can also be obtained by filtering molten metal through fine-grained ceramics. Using a filter with an average particle size of 2-35 microns and a layer thickness of 105 microns, it is possible to remove nearly 90% of the oxides and 85% of the metal compounds present in za4-1 alloy. When in use, the filter is placed in the bell jar and heated to 5000C before being placed in the holding furnace or ladle. Rare earth elements have chemical properties that are quite active. They have the ability to form compounds with low relative density and high melting point when combined with impurities such as O, N, and h. These compounds, as well as slag, are easily removed from liquid metal.

    3. Refining Agent
    In various casting furnaces, a refining agent can refine, protect, and remove slag from molten metal, resulting in the production of high purity products and the purification of the melt. Hexachloroethane, zinc oxide, rare earth elements, inert gas, and other refining agents are commonly used in the refinement of zinc alloys. Before refining, it is necessary to coat the tools in order to prevent impurities, particularly iron, from infiltrating into the liquid alloy. The coating is primarily composed of zinc oxide, fossil powder, water glass, and water.

    – Hexachloroethane is non-hygroscopic, non-remelting, less corrosive, and easy to preserve. It can be used in a variety of casting alloys in place of chloride refining agent.
    - Zinc oxide flux is a type of casting raw material and auxiliary material that is primarily used in the removal of slag from zinc alloy castings and the refining of zinc alloy. Before using zinc oxide, it must be remelted and dried in a drying oven at 100-130 degrees Celsius. It is used in Zn-containing alloys as well as alloys where there are no strict requirements on Zn impurities. Its disadvantage is that a large number of harmful gases are produced during the manufacturing process, and the level of environmental protection is extremely low. The slag removal and refining effect of zinc alloy flux is insufficient, resulting in the impurities and bubbles in the alloy liquid not being completely removed, as well as an increase in the waste products of zinc die castings.
    Rare earth elements have chemical properties that are quite active.  They can combine with impurities such as 0, N, and h to form compounds with a low relative density and a high melting point. Typically, these compounds are easily removed from liquid metal along with slag in order to achieve a refining effect.
    - Inert gases, such as nitrogen or nitrogen dioxide, are low-cost and pollution-free, and they are used in a variety of alloys.

    The refining agent has a favorable effect on the degassing and slag removal of the alloy liquid. It has been reported that when the chlorination press is pressed into the bell jar at 450-470 degrees Celsius, nearly 80% of the oxides and 70% of the intermetallic compounds in the zinc alloy liquid are removed, thereby ensuring the quality of the alloy. However, experiments have shown that the use of chlorination (0.12% of the total amount of refining metal) will increase the melting loss rate of the alloy, as well as produce a significant amount of smoke and ammonia gas during the process, both of which will worsen the operating environment. In many cases, static clarification is the only method that can be used to produce ingots with a compact cross-section structure and free of slag and inclusions. As a result, the slag-making operation and the amount of chlorination that must be added can be calculated based on the amount of recycled materials used.